How will Martha Jones fit into Doctor Who?

WARNING: This posting contains spoilers for series two of Doctor Who! Right, on we go. It's been announced that Freema Agyeman will join the TARDIS for the third series of Doctor Who, to be broadcast next year on BBC1. The new companion is called Martha Jones and I know absolutely nothing more about her beyond that. Everything that follows is merely speculation, okay? Good.

We've just said goodbye to Rose Tyler, the Doctor's council estate companion, plucked from contemporary Earth. Her time in TARDIS also gave the show an extended family, with Rose's mum Jackie, sometime boyfriend Mickey and often dead dad Pete. All of this grounded the show in the here and now, procuring massive audience identification and helping create a family audience for the Doctor's adventures. With a contemporary companion, taking Rose into past or future gave everything a novelty, a freshness.

The question now is how will the new companion affect that dynamic of the show? Will Martha be cut from much the same cloth as Rose, or will the programme makers opt for something more radical? Perhaps Martha will be all ASBOs and attitude, an angry young woman searching for her place in the universe. Perhaps she'll be plucked from the past, so bringing her to contemporary Earth [well, Cardiff, for the most part] will make the commonplace seem new to the viewer, seeing it afresh through Martha's eyes. The same effect could be achieved by having her come from humanity's future, or from another planet - perhaps an Earth colony of tomorrow.

In its first incarnation, Doctor Who ran for 26 years on British TV. During that time, the Doctor's companions were mostly required to ask questions that elicited exposition or fall into jeopardy. The best companions stood out because of their particular qualities. Sarah Jane Smith was an investigative journalist and proto-feminist of sorts, who stood up for herself while asking impertinent questions. Leela was a savage from a human colony, who underwent a Pygmalion-esque transition. Romana was a Time Lady, making her the Doctor's equal - and sometimes his superior. Ace was a troubled London teenager who wanted to escape. More recently, Rose was a bored young woman from Londonn who wanted to escape, but still loved her family - a softened, more nuanced progression of Ace.

So, will Martha Jones resemble any of these past companions, or will she be something entirely fresh and different? What do you think?